Surf PI Pro

[nonkapo]

I think i stuck without osciloscope:-(. Have the strange feeling neither the offset trimmer work, neither the delay pot(offset measured 0.37V). Volume, -treshold and sensitivity are ok. MTB brake disc detected at 15cm, nailcutter detected at only 5cm. Will try tomorrow new coil. Meantime any help or direction will be appreciated. Basket coil from UTP6 24 awg, induction 370uH, 1.6 ohm resistance, dumping resistor 370 ohm.

[Andi68]

I mean, with a basket coil, the magnetic field is not optimal

[dbanner]

I think i stuck without osciloscope:-(. Have the strange feeling neither the offset trimmer work, neither the delay pot(offset measured 0.37V). Volume, -treshold and sensitivity are ok. MTB brake disc detected at 15cm, nailcutter detected at only 5cm. Will try tomorrow new coil. Meantime any help or direction will be appreciated. Basket coil from UTP6 24 awg, induction 370uH, 1.6 ohm resistance, dumping resistor 370 ohm.

Use the damping tool to setup the coil. Then she will respond with better sensitivity.
You can setup without scope, just wave US nickel and adjust damping resistance for max sensitivity of coil, then the other metals will be ok.
If you then put scope to see waveform, surprise, surprise, she is well set.
The offset trimmer must be set for 0 voltage of pin on IC. With input disconnected.
If you don't see voltage moving when turning offset trimmer, then something is not right with circuit.

[nonkapo]

Use the damping tool to setup the coil. Then she will respond with better sensitivity.
You can setup without scope, just wave US nickel and adjust damping resistance for max sensitivity of coil, then the other metals will be ok.
If you then put scope to see waveform, surprise, surprise, she is well set.
The offset trimmer must be set for 0 voltage of pin on IC. With input disconnected.
If you don't see voltage moving when turning offset trimmer, then something is not right with circuit.

What do you mean with input disconnected? 5534 input? As per what i know the coil should be connected right?
About the damping tool i try but having in hand only 1k wirewind pot, so put it in series with 390Ohm but it does not change anything. Yesterday evening i try two more coils with the same result. So delay pot does not change anything and the offset trimmer turned all the way does not change the offset - it stays in 0.36-0.38 range. Forget to mention the power source which is not battery but probably PSU 12volt.

[dbanner]

Wire wound pot is good for this purpose. You must see significant change in voltage when adjusting offset trimmer. Something must be wrong with the circuit or the chip itself.
There was discussion the issue of adjustment of offset voltage, how it supposed to be done proper way. It is somewhere in forum but I can't remember where to look.
There is 22k resistor feeding center pin of trimmer. Make sure it is properly connected on PCB. From supply voltage to center pin. Make certain that it is correct value.
Can you put pics of your PCB. This could help.
Your coils are good and not the problem. The culprit is on PCB.

[nonkapo]

Thanks. I've checked three times the values and they all seem ok. One other thing i checked was Jose's advice to put 3k3 resistor on the 2N3906. However no difference. Will get some photos until it is not dark and let you know. After measuring again, the resistor R11 is 22k, 5,1 volt before, 4.3volts after(going to the trimmer). Meantime 5534 was replaced without result. Something else sort of bother me now. I think i mess up some zener diodes with my 4148. I start thinking i put zeners instead of 4148. They are too tiny for me to be able reading the markings.

[Andi68]

Do not replace 1n4148 with Zener diodes

[nonkapo]

Here are the pics

[nonkapo]

I think the only option is to buy some more 5534, possibly from different sources as i do with the rest of the components and give it a try. There is an extensive thread here about counterfeit 5534 which does not let offset adjustment. i will keep you updated about.

[Andi68]

I also advise you to inspect the solder side of the board very closely

[dbanner]

I think the only option is to buy some more 5534, possibly from different sources as i do with the rest of the components and give it a try. There is an extensive thread here about counterfeit 5534 which does not let offset adjustment. i will keep you updated about.

I you mentioned this, I have fake 5534 chips, offset don't do nothing. I will put photo of mine fake ones. When I replaced with genuine one, sensitivity was great. With fake chips, sensitivity was very poor. Something like what you are experiencing.

[nonkapo]

O mighty god, this is what i should do at the begining. It will save me from two sleepless days off:-))). But as any human i was suspicious about my self. The fake one i heard of are with Texas instruments logo and exactly the same are the one i have in possesion.
I think tomorrow a visit to Dubai will reveal where the truth is.
Thanks again

[Andi68]

And sometimes these trimmers break down too fast

[dbanner]

O mighty god, this is what i should do at the begining. It will save me from two sleepless days off:-))). But as any human i was suspicious about my self. The fake one i heard of are with Texas instruments logo and exactly the same are the one i have in possesion.
I think tomorrow a visit to Dubai will reveal where the truth is.
Thanks again

Yes! My fake ones are Texas instruments logo!
My good ones are Phillips. Here is photo of good Phillips chip I used.

[dbanner]

Here is photo of almost same as my fake ones
The fake ones I have look like these except that they have the "U" notch on top as is normal.